Learn Hardcore Japanese: watasi ha syuumatu ni tomodati to issyo ni geemu wo simasu. - I play games with a friend on the weekend.

The true grammatical subject can be left out (here it’s understood as “I”), but は just marks what the sentence is about. In many simple sentences, topic and subject are the same person/thing, which makes it feel like a “subject marker,” but conceptually they’re different.

You could replace 私 with something else:

弟は週末にゲームをします。
As for my little brother, he plays games on weekends.

Why is there に after 週末? What does 週末に mean exactly?

The particle に after a time expression marks when something happens.

週末 = weekend
週末に = on the weekend / at the weekend

So 週末に tells us the time of the action ゲームをします (play games).

In general, you use に with specific points in time:

３時に = at 3 o’clock
日曜日に = on Sunday
誕生日に = on (my) birthday

Some very broad time words often drop に (like 毎日, 明日), but 週末に with に is perfectly natural and common.

There is another に in 一緒に. Is that the same に as in 週末に?

Grammatically they are both the particle に, but their roles feel different:

週末に: に marks a time point → on/at the weekend.
一緒に: 一緒 (together) + に behaves almost like a fixed adverbial phrase, meaning together (with someone).

You can think of 一緒に as one chunk:

一緒に行きます。 – I’ll go together (with you/them).
友達と一緒に勉強します。 – I study together with my friend(s).

So yes, it’s the same particle, but in 一緒に it has become part of a very common pattern that you can memorize as “together”.

What does と after 友達 mean? Isn’t と mainly “and”?

と has two main beginner-friendly uses:

“and” when listing things
- りんごとバナナ = apples and bananas
“with (someone)” as a partner marker
- 友達と行きます。 = I’ll go with a friend.
- 彼女と話します。 = I talk with her.

In 友達と一緒にゲームをします, the と shows that 友達 is your companion/partner for the action.
So here, it’s best understood as “with (friend)”, not “and” in a list.

What does を do in ゲームをします? Why not just ゲームします?

を marks the direct object of the verb – the thing the action is done to.

ゲーム = game(s)
ゲームをする / ゲームをします = to do/play a game

So ゲームをします literally means do game(s).

In casual spoken Japanese, people often drop を:

ゲームする? – Wanna play (a) game?
ゲームします。 – I play games.

But grammatically, ゲームをします is the full, clear form, and it’s very natural in polite speech or in writing.

Why is the verb します and not する or something like やる?

する is the dictionary/plain form, and します is its polite form.

ゲームをする。 – (plain/casual) I play games.
ゲームをします。 – (polite) I play games.

やる can also mean “to do/play,” and ゲームをやる is quite casual and colloquial. Compared with する:

ゲームをする: neutral, standard
ゲームをやる: more casual, can sound a bit rough depending on context/speaker

In a textbook-style, polite sentence like this one, します is the expected choice.

Can I leave out 私 and just say 週末に友達と一緒にゲームをします?

Yes, and that’s actually very natural in real Japanese.

Japanese often omits pronouns like 私, あなた when they’re obvious from context.

If you are talking about your own routine, 週末に友達と一緒にゲームをします。 will normally be understood as “I play games with my friend(s) on weekends.”
You only need 私 when you want to explicitly contrast or clarify who you’re talking about, e.g.:
- 私は週末にゲームをしますが、弟はしません。
  I play games on weekends, but my little brother doesn’t.

So in everyday conversation, the shorter version without 私 is very common.

How can I tell whether 友達 means “friend” or “friends”? There’s no plural marker.

Japanese nouns generally don’t mark singular vs. plural.

友達 can mean a friend, the friend, or friends, depending on context.

In 友達と一緒にゲームをします, possible natural translations are:

I play games with a friend on weekends.
I play games with my friend on weekends.
I play games with friends on weekends.

If you really want to clarify plural, you can say, for example:

友達たちと一緒に… (friends – but 友達たち can sound a bit childish or overly literal)
何人かの友達と… (with several friends)
友人たちと… (with friends – more formal/neutral word)

But most of the time, Japanese just relies on context.

What’s the difference between 友達とゲームをします and 友達と一緒にゲームをします?

Both can mean “I play games with my friend(s),” but the nuance is slightly different:

友達とゲームをします。
→ States that your partner in the action is your friend(s).
友達と一緒にゲームをします。
→ Emphasizes the idea of doing it together, not separately.

In practice:

友達とゲームをします already implies “together” in most contexts.
Adding 一緒に makes that “together” feeling a bit more explicit or stronger, and sounds very natural and friendly.

Why is the tense します (non-past)? How can it mean a habitual action like “(I) play (regularly)”?

Japanese non-past (the form that ends in -ます / -る) covers both present and future.

In this sentence, it’s interpreted as habitual present because of context:

週末に – “on weekends” suggests a repeated, regular action.
So ゲームをします here = “(I) play games (as a habit).”

Compare:

明日、友達とゲームをします。
→ I will play games with my friend(s) tomorrow. (future)
毎週末、友達とゲームをします。
→ I play games with my friend(s) every weekend. (habitual present)

The same non-past form can be understood as present or future depending on the time expressions around it.

Could I change the word order, like 週末に私は友達と一緒にゲームをします? Is that still correct?

Yes, that’s grammatically correct. Japanese word order is relatively flexible as long as:

The verb (here します) is at the end, and
The particles stay attached to the right words (私は, 週末に, 友達と, 一緒に, ゲームを).

Possible variants include:

週末に友達と一緒にゲームをします。
私は友達と一緒に週末にゲームをします。
友達と一緒に週末にゲームをします。 (dropping 私)

They’re all understandable, but the default/most natural is usually:

(私は) 週末に友達と一緒にゲームをします。

Shuffling too much can sound marked or unnatural, so it’s best to stick close to that order as a learner.

Why use は with 私 and not が? Would 私が週末に友達と一緒にゲームをします be wrong?

私が週末に友達と一緒にゲームをします is grammatically correct, but the nuance is different:

私は週末に友達と一緒にゲームをします。
→ As for me, on weekends, I play games with my friend(s).
Neutral statement about your own routine; は sets “me” as the topic.
私が週末に友達と一緒にゲームをします。
→ I (as opposed to someone else) am the one who plays games on weekends.
This often implies contrast or emphasis, like:
- Not my brother, I am the one who does it.
- Or answering the question “Who plays games on weekends?”

So for a simple self-introduction-type sentence about your habit, 私は… is much more natural than 私が….